Method of making ultra thin walled wire reinforced endotracheal tubing

ABSTRACT

An ultra thin walled wire reinforced endotracheal tubing includes a thin walled tubing comprising a polymeric material having a spring material incorporated therewith. Utilization of the spring wire material in combination with polymeric material results in a reduced wall thickness which results in a significant decrease in resistance to air flow through the endotracheal tubing. The endotracheal tubing of the present invention is made by depositing a dissolvable polymeric material on a rotating mandrel in. successive layers. A spring material is also applied around the mandrel to produce the ultra thin walled wire reinforced endotracheal tubing. By controlling the rate of deposition of polymeric material along the length of the mandrel, different wall thicknesses of tubing may be achieved.

This application is a continuation of application Ser. No. 07/758,824filed Sep. 12, 1991, and now abandoned.

FIELD OF INVENTION

The present invention is directed to an ultra thin walled wirereinforced endotracheal tubing. The ultra thin walled tubing comprises apolymer tube having incorporated therewith a stainless steel springmaterial. The method of making the tubing comprises coating a rotatingTeflon® coated steel mandrel with a polymer material and incorporating astainless steel spring material therewith. The apparatus includes apolymer supply unit, a pump means to meter the polymer material onto therotating mandrel and means to dry the polymer as supplied to themandrel. The ultra thin walled endotracheal tubing reduces airwayresistance when compared to standard endotracheal tubes which permitsestablishment of artificial airways other than mechanical ventilators.

BACKGROUND ART

Endotracheal tubes are widely used in anesthesia and critical caremedicine. The endotracheal tube provides access to the upper airways forcontrolled, assisted ventilation or spontaneous unassisted ventilationwith positive end expiratory pressure.

One of the drawbacks of inserting an endotracheal tube into an upperairway of a patient results in the reduction of the lumen of the airway.One manner in which the lumen is reduced is the inability to use thelargest possible endotracheal tube for a given patient withoutsubjecting the patient to increased risks. Generally, it is notadvisable to insert the largest possible endotracheal tube in thepatient since such an attempt will entail many trials and errors whichmay take additional time, such additional time to be avoided, especiallyin critical care situations.

In addition, and to maintain endotracheal wall stability, the wallthickness is required having sufficient strength to be safely handled bythe using physician or technician. At present, adult endotracheal tubesrange between 7 to 9 millimeters in internal diameter, the total wallthickness ranging between 1.4 and 1.5 millimeters. For newbornendotracheal tubes, the decrease in lumen internal diameter as a resultof the required wall thickness amounts to approximately 0.5 millimetersor more.

Any decrease in the lumen due to wall thickness has a profound effect onthe airway resistance, since the resistance to air flow is inverselyproportional to the fourth power of the radius.

As a result of the deficiencies in prior art endotracheal tubes, a needhas developed to provide an endotracheal tube having reduced airwayresistance so as to facilitate establishment of artificial airways otherthan those using mechanical ventilators.

Conventional technology used in the fabrication of blood catheters useseither extrusion or dip coating onto mandrels. Extrusion technology hasthe advantage of low cost, but has little flexibility. With extrusion,the resulting thin wall catheters are rather stiff and are liable tokink or bend to obstruct the inner passageway. The dip coating techniqueused for currently available catheters and tubes is not reproducible inthin wall gauges and, therefore, wall thickness remain substantial.

In response to this need, the present invention provides an ultra thinwalled wire reinforced endotracheal tube which provides reduced airwayresistance to permit easier breathing by a patient. The ultra thinwalled endotracheal tube comprises a polymer having incorporatedtherewith a stainless steel spring material to form a continuous tubing.The combination of the polymer and stainless steel spring materialprovides an ultra thin wall of the tubing which permits the use of anendotracheal tube having similar diameters as prior art tubings but withincreased internal diameters and resultant reductions in airwayresistance.

SUMMARY OF THE INVENTION

It is accordingly a first object of the present invention to provide anultra thin walled wire reinforced endotracheal tubing.

It is a further object of the present invention to provide an apparatusfor and a method of making ultra thin walled wire reinforcedendotracheal tubing.

It is a still further object of the present invention to provide thinwalled endotracheal tubing which provides reduced airway resistance whenused to establish an artificial airway by having increased innerdiameters.

It is a yet further object of the present invention to provide ultrathin walled wire reinforced endotracheal tubing which permits a patientusing the tubing to breathe in a more relaxed fashion so as not tobecome exhausted or tired by attempting to breathe through smallerdiameter prior art endotracheal tubes.

In satisfaction of the foregoing objects and advantages, there isprovided an ultra thin walled wire reinforced endotracheal tubing whichcomprises a polymeric material having a stainless spring materialincorporated therewith. The combination of the polymeric material andstainless steel spring material permits the endotracheal tube to have anultra thin wall diameter to provide for an increased air passageway andreduced airway resistance.

An apparatus is provided for making the ultra thin walled wirereinforced endotracheal tubing and includes a coated steel rod, a lathemeans for rotating the rod, a liquid polymer supply source, a means formetering the liquid polymer along the length of the steel rod andcontrol means for controlling the thickness of the polymer as applied tothe rod to achieve a desired wall diameter. In addition, the stainlesssteel spring material may be pre-wound and slid over the coated steelrod or, alternatively, means may be provided to coil the spring materialaround the coated steel rod.

The method of making the ultra thin walled wire reinforced endotrachealtubing generally includes the steps of applying a dissolved polymer tothe coated steel rod, incorporating the stainless steel spring materialaround the polymer coated steel rod, providing an additional amount ofpolymeric material around the spring material and removing the tubingfrom the mandrel. Additional embodiments include varying the sequence ofapplications of polymer material and stainless steel spring material tothe rod. The as-applied polymeric material may also be subjected to adrying step using a strip heater with baffles to accelerate themanufacturing process.

BRIEF DESCRIPTION OF DRAWINGS

Reference is now made to the Drawings accompanying the application,wherein:

FIG. 1 shows a schematic representation of one embodiment of theapparatus utilized for making the ultra thin walled wire reinforcedendotracheal tubing;

FIG. 2A shows an end view of a prior art endotracheal tube;

FIG. 2B shows an end view of an endotracheal tube according to thepresent invention;

FIG. 3A shows an end view of another prior art endotracheal tube;

FIG. 3B shows an end view of a smaller size ultra thin walled wirereinforced endotracheal tube of the present invention;

FIG. 4 shows a graph comparing air resistance in the inventive ultrathin walled endotracheal tube as compared to prior art endotrachealtubes; and

FIG. 5 shows an exemplary ultra thin walled wire reinforced endotrachealtube showing the spring material incorporated in the endotracheal tubingwall.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is concerned with endotracheal tubes which provideartificial airways in applications such as anesthesia and criticalmedicine. The ultra thin walled wire reinforced endotracheal tube of thepresent invention offers advantages over prior art tubing by providing,for the same outer diameter of tubing, and increased inner diameter andreduced airway resistance. By incorporating a stainless steel springmaterial with a polymeric material in a thin walled tubingconfiguration, an endotracheal tube is provided which has sufficientstrength to be safely handled by a user.

By providing low air resistance endotracheal tube, whereby patientbreathing is made easier, patients may be able to utilize a simplermeans of respiratory assistance such as continuous positive airwaypressure (CPAP) rather mechanical ventilation means.

In the newborn patient population, the lowering of airway resistance isof vital importance since newborns are more likely to become exhaustedor have further difficulty in breathing by using prior art endotrachealtube having significant airway resistance. By utilizing the inventiveultra thin wall wire reinforced endotracheal tubes in newborn patientapplication, significant reductions in airway resistance are attainable.

In addition, developments and other alternatives for mechanicalventilation such as intratracheal pulmonary ventilation which include areduction in dead space ventilation and a decrease in airway pressurefavor the utilization of establishment of artificial airways havingreduced resistance to air flow. As will be described hereinafter, theinventive tubing reduces the wall thickness by 50-80%, thereby resultingin a two- to four-fold decrease in air flow resistance.

With reference now to FIG. 1, a schematic representation of an apparatusadapted for making ultra thin walled wire reinforced endotracheal tubeis illustrated. The apparatus is generally designated by the referencenumeral 10 and is seen to include a cylindrical mandrel 1 having arelease agent coating on the surface 2 thereof. The release agent 2 isdesigned to facilitate removal of the ultra thin walled wire reinforcedendotracheal tubing from the cylindrical mandrel 1. The release agentmay be any agent known in the art such as Teflon®. The cylindricalmandrel may be made of any material having sufficient strength toprovide support for the tubing, preferably a steel rod.

The cylindrical mandrel is connected to a lathe means 3 which includesdrive means therewith to rotate the mandrel at a predetermined speed. Ofcourse, any known means capable of rotating a cylindrical mandrel may beutilized in substitution for the lathe 3.

The apparatus for making the ultra thin walled wire reinforceendotracheal tubing also includes a polymer source means 5 whichsupplies a dissolvable polymer such as polyurethane Lycra® underpressure to a metering pump 9 via the line 7. The polymer source meansmay be a closed container including a source of inert gas to provide thepressure to supply the dissolved polymer to the metering pumping 9.Preferably, the source of the pressure is a dry nitrogen or other inertgas.

The metering pump 9 includes a nozzle 11 made out of a flexible tubingsuch as Teflon®. The tubing 11 should have sufficient flexibility andthickness to follow the contours of the cylindrical mandrel 1 and floaton the polymer layer as it emerges from the nozzle. The flexibility ofthe tubing 1 may be enhanced by the addition of a spring materialsurrounding the tubing. The metering pump 9 may be a gear fluid pumpdesigned to meter a solution of polymer onto the mandrel.

The polymer source means 5 and metering pump means 9 also include across feed means which permits the source means 5, metering means 9 andnozzle 11 to traverse the length of the mandrel 1. As illustrated by thereference numeral 21 in FIG. 1, the source means 5, metering pump 9 andnozzle 11 are displaced along the longitudinal axis of the cylindricalmandrel 1. The longitudinal movement of the nozzle 11 permits thatpolymer to be continuous applied to the mandrel over a preselectedpattern.

A control means 13 is provided that regulates the deposition of thepolymer on the mandrel 1. The control means is connected to the polymersource means 5 via the line 15, the metering pump 9 via the line 17 andthe lathe 3 via the line 19. By controlling the rotation of the mandrel1 via the lathe 3 and the amount of polymer deposited on the mandrel 1,the thickness of polymer applied to the mandrel or wall thickness of theultra thin walled and wire reinforced endotracheal tubing may becontrolled and varied. The control means 13 also provides control overlongitudinal traversing of the nozzle 11 and associated components andthe cylindrical mandrel 1. It should be understood that, although thenozzle 11, metering pump 9 and polymer source means 5 are depicted aslongitudinally traversing the length of the cylindrical mandrel 1, inanother embodiment, the polymer source means 5 may be stationery withthe metering pump 9 and nozzle 11 traversing the length of themandrel 1. It should be understood that the mechanism for providing thelongitudinal traversing movement of either the metering pump 9 andnozzle 11 or these components with the polymer source means 5 are wellrecognized in the prior art. For example, these components may belongitudinally traversed using a drive means and rack and piniongearing.

The apparatus 10 also includes a heating means 23 which supplies heatsuch as hot air to the mandrel 1 to dry the polymer solution afterdeposition on the mandrel.

The heating means may a strip heater or other known heating means. Theheating means 23 may also include individually adjustable baffles 25which facilitate directing the hot air toward the mandrel 1. Theadjustable feature of the baffles 25 permit varying the amount of dryingair along the length of the mandrel 1. For example, when producing atapered endotracheal tube, certain areas of the tube having increasedwall thickness require a higher heat input for drying purposes. In thissituation, the individually adjustable baffles are arranged to directmore hot air to the portion of the cylindrical mandrel having theendotracheal tube with increased wall thickness.

FIG. 1 also depicts a coil spring 27 which is designed to be insertedover the Teflon® coated cylindrical mandrel 1. The spring 27 may bemanually inserted over the rod or, alternatively, by known mechanicalmeans. As an alternative embodiment, the spring material may be in theform of an unwound wire or flat material and be wound around thecylindrical mandrel in a known fashion. As will be describedhereinafter, the spring 27 may be applied to the mandrel 1 after orduring the deposition of the polymeric material.

The method of making the ultra thin walled wire reinforced endotrachealtubing will now be described. In the first embodiment, a polymericmaterial such as a polyurethane Lycra® is dissolved in a compatiblesolvent. A typical concentration of polymeric material would rangebetween 25-28 weight percent polymer in the solvent. This range is onlyexemplary and more or less concentrations of polymeric material may beutilized depending on the particular polymer being employed. Thedissolved polymer is supplied to a metering pump under pressure such asdry nitrogen. The metering pump, such as a fluid gear pump, meters thedissolved polymer unto the rotating surface of the mandrel while thenozzle traverses the length of the cylindrical mandrel. The depositedpolymer is permitted to air dry, or alternatively, dry by application ofa source of heat such as a strip heater or the like. This sequence maybe repeated if an increased thickness of polymeric material is desiredon the surface of the cylindrical mandrel.

By choosing a particular rate of deposition of polymeric material, thesolvent evaporation rate can be optimized such that one layer of polymercan be deposited onto the previously deposited and dried layer to buildup thickness. In a further embodiment, successive deposition of severallayers of polymeric solution may be performed while traversing thecylindrical mandrel on a single run. In this embodiment, a plurality ofnozzles may be utilized which are spaced apart from each other such thatfollowing nozzles are depositing polymeric material to an already driedpolymeric material layer.

Once the initial layer or layers of polymeric solution are deposited onthe cylindrical mandrel a spring material, preferably a stainless steelspring, is applied to the cylindrical mandrel. In one embodiment, thestainless steel spring may be in an uncoiled configuration, either flator round in size, and wound around the polymer-coated mandrel by knownmechanical means. Alternatively, the stainless steel spring may beprovided in a pre-coiled configuration and inserted over the mandrel.

The choice of winding per inch for the spring or the diameter orcross-sectional area of the spring material may vary depending upon thedesired spring properties and flexibility of the ultra thin walled wirereinforced endotracheal tube. Furthermore, it should be understood thatthe spring material cross-sectional area, or diameter if the springmaterial is round, is sized to provide the ultra thin walled wirereinforced endotracheal tubing having a reduced wall thickness whilemaintaining sufficient strength to avoid kinking or bending duringhandling and subsequent constriction of an airway passage.

Once the spring wire is applied to the mandrel, further deposition ofpolymeric material may be performed to yield a smooth outside surfacehaving the desired final diameter.

In a further embodiment, the spring material may be wound around themandrel or inserted thereover, simultaneously with the application ofthe polymer solution.

With reference to FIGS. 2A and 2B, a comparison is illustrated betweenprior art endotracheal tubes and the ultra thin walled wire reinforcedendotracheal tubing of the present invention. As can be seen from FIG.2A, the prior art endotracheal tube having an outer diameter of 10.7millimeters has an inner diameter of 7.5 millimeters due to the wallthickness of 1.6 millimeters. In contrast, the ultra thin wall wirereinforced endotracheal tubing of the present invention may be madehaving the same outer diameter of 10.7 millimeters but with an increasedinner diameter of 10.2 millimeters as a result of the reduced wallthickness of 0.25 millimeters.

Referring to FIGS. 3A and 3B, a similar comparison is made wherein theprior art endotracheal tubing 33 is compared to the ultra thin walledwire reinforced endotracheal tubing 35 of the present invention. In thismanner, the prior art endotracheal tubing 33 having an outer diameter of9.3 millimeters has an inner diameter of 6.5 millimeters. The ultra thinwalled wire reinforced endotracheal tubing 35 has an increase in theinner diameter to 8.8 millimeters for the same 9.3 millimeter outsidediameter.

With reference now to FIG. 4, a graph is depicted which comparesstandard endotracheal tubes such as those depicted in FIG. 2A and 3Awith the ultra thin walled wire reinforced tubing of the presentinvention having a wall thickness of approximately 0.25 millimeters. Thegraph compares the resistance of the inventive thin walled endotrachealtubing as a percent of the air resistance of the standard endotrachealtubing for a range of endotracheal tubing based upon inner diameters. Ascan be seen from the graph in FIG. 4, the inventive thin walledendotracheal tubing results in a substantial decrease in resistance ascompared to prior art endotracheal tubing. In addition, air flowresistance is further lowered for smaller sized endotracheal tubes whichprovides reduced air resistance in endotracheal tubing adapted fornewborn patients.

With reference now to FIG. 5, an exemplary Ultra thin walled wirereinforced endotracheal tubing is generally designated by the referencenumeral 40. The thin walled wire reinforced endotracheal tubing includesa tubing wall 41 having an inner surface 43 and outer surface 45.Incorporated within the tubing wall 41 is a spring 47. The diameter ofthe spring material 47 is sized in conjunction with the applied layersof polymeric material to provide the minimum wall thickness whilemaintaining sufficient strength to permit handling of the endotrachealtube. As disclosed above, a wall thickness of about 0.25 millimeters isattainable using the inventive method and apparatus for making the ultrathin walled wire reinforced endotracheal tubing. The wall thickness ofabout 0.25 mm is a preferred thickness with the wall thickness rangingbetween about 0.1 mm and 0.5 mm. A preferred range for the wallthickness includes between about 0.15 mm and 0.35 mm. For a given wallthickness of 0.25 millimeters, it should be understood that the diameterof the wire spring material is less than the wall thickness to provide apolymeric layer along the inner and outer surfaces, 43 and 45respectively of the tube 40. Alternatively, the wire spring materialwhen positioned on the cylindrical mandrel prior to deposition ofpolymeric material may form part of the inner surface 43 of the tubing40.

The apparatus and method of making the ultra thin walled wire reinforcedendotracheal tubing provides a endotracheal tube having a thin wallthickness not attainable in prior art endotracheal tube making apparatusor method. The inventive apparatus and method also provide flexibilityin adapting the manufacture of the inventive endotracheal tubing forvarious configurations for operating conditions such as an eccentric orslightly out of round mandrel. By having the nozzle of the metering pump9 float or follow the contour of the mandrel, any slight out ofroundness and/or eccentricity of the mandrel can be easily accommodatedwithout effecting the quality of the tube.

In addition, the method of applying the polymer solution along thelength of the mandrel permits programming of the control means toachieve different tubing configuration. For example, by increasing theflow rate of the dissolved polymer or reducing the rotation of themandrel in conjunction with controlling the travel of the nozzle 11along the mandrel, varying thicknesses of wall tubing may be obtained.By programming of more layers of different thicknesses on differentparts of the mandrel, utilizing the control means, tapered endotrachealtubes may be manufactured. Alternatively, the mandrel 1 may be madehaving a tapered configuration wherein a tapered spring material may beused in conjunction with a uniform coating to produce a tapered tubehaving a uniform wall thickness.

As such, an invention has been disclosed in terms of preferredembodiments which fulfill each and every one of the objects of thepresent invention as set forth hereinabove and provides a new andimproved ultra thin walled wire reinforced endotracheal tubing as wellas an apparatus and method for manufacturing thereof.

Of course, various changes, modifications and alterations in theteachings of the present invention may be contemplated by those skilledin the art without departing from the intended spirit and scope thereof.As such, it is intended that the present invention only be limited bythe terms of the appended claims.

I claim:
 1. A method of making an ultra thin walled wire reinforcedendotracheal tubing comprising the steps of:a) providing a polymericmaterial solution; b) providing a mandrel; c) flowing a metered amountof said polymeric material solution along said mandrel through a nozzlefollowing a contour of said mandrel while rotating said mandrel therebyforming at least one layer of polymeric material; and d) depositing aspring wire onto and around said at least one layer followed by flowingsaid polymeric material solution through said nozzle and along saidmandrel wherein said nozzle forces said polymeric material solutionaround the spring wire while rotating said mandrel thereby forminganother layer of said polymeric material over said spring wire and saidat least one layer, and thus forming a tubular assembly; e) and removingsaid tubular assembly from said mandrel.
 2. The method claim 1 whereinat least one said pumping steps further comprises the step of forming aplurality of layers of said polymeric material solution.
 3. The methodof claim 1 wherein the step of providing a polymeric material solutionincludes the step of providing a polyurethane dissolved in a solvent. 4.The method claim 1 wherein said at least one layer, said spring wire andsaid another layer form a wall of said tubular assembly, said wallhaving a wall thickness ranging between 0.10 millimeters and 0.50millimeters.
 5. The method of claim 1 further comprising the step ofcontrolling the thickness of said at least one layer and said anotherlayer by regulating said metering and rotating steps.
 6. The method ofclaim 1 wherein the forming of said at least one layer of polymericmaterial includes drying said polymeric material solution.
 7. The methodof claim 1 further comprising the step of varying the outer diameter ofsaid tubular assembly by regulating at least one of said pumping step,said rotating step, and selection of said spring wire.
 8. A method ofmaking an ultra thin walled wire reinforced endotracheal tubingcomprising the steps of:a) providing a polymeric material solution; b)providing a mandrel; c) flowing a metered amount of said polymericmaterial solution along said mandrel through a nozzle following acontour of said mandrel while rotating said mandrel thereby forming atleast one layer of polymeric material; and d) depositing a spring wireonto and around said at least one layer while simultaneously forminganother layer of said polymeric material over said spring wire and saidat least one layer by flowing a metered amount of said polymericmaterial solution through said nozzle and along said mandrel whilerotating said mandrel wherein said nozzle forces said polymeric materialsolution around said spring wire thus forming a tubular assembly; and e)removing said tubular assembly from said mandrel.
 9. The method of claim3 wherein the forming of said at least one layer of polymeric materialincludes evaporating said solvent.
 10. The method of claim 9 wherein atleast one said pumping steps further comprises the step of forming aplurality of layers of said polymeric material solution.
 11. The methodof claim 8 wherein the step of providing a polymeric material solutionfurther comprises the step of providing a polyurethane dissolved in asolvent.
 12. The method of claim 11 wherein the forming of said at leastone layer of polymeric material includes evaporating said solvent. 13.The method of claim 9 wherein said at least one layer, said spring wireand said another layer form a wall of said tubular assembly, said wallhaving a wall thickness ranging between 0.10 millimeters and 0.50millimeters.
 14. The method of claim 9 further comprising the step ofcontrolling the thickness of at least one of said at least one layer ofsaid another layer by regulating said pumping and rotating steps. 15.The method of claim 9 wherein the forming of said at least one layer ofpolymeric material includes drying said polymeric material solution. 16.The method of claim 9 further comprising the step of varying the outerdiameter of said tubular assembly by regulating at least one of saidpumping step, said rotating step, and selection of said spring wire.